Recent work has led to the discovery of a class of growth-associated proteins, called GAPs, whose expression is selectively enhanced in regenerating and developing neurons of some species. The purpose of this investigation is to study the cellular role of these growth-associated proteins, and in particular to determine whether tje abo;otu pf a meirpm tp regenerate depends on its ability to induce their synthesis. There are five related objectives. The first objective is to determine, by means of a limited phylogenetic survey, whether these proteins appear in CNS neurons lacking the capability to regenerate, or whether they occur only in growing or regenerating neurons. Two very sensitive and powerful techniques will be employed to detect and quantitate these proteins: computer-analyzed 2-dimensional gel electrophoresis, and immunological techniques. The second objective is to determine the cellular localization of GAPs, using EM immunocytochemical localization methods. The third objective is to characterize the major distinguishing characteristics of GAPs, and the fourth is to investigate the cellular functions of GAPs, by correlating the kinetics of GAP expression with different phases of axonal growth in developing and regenerating systems. The last objective is to determine how the expression of GAPs is regulated. We plan to study the effects of several likely regulatory molecules on GAP synthesis, including nerve growth factor (NGF) and cyclic AMP. The site of regulation (transcriptional, translational, of post- translational) will be determined with inhibitors of RNA and protein synthesis. Finally, specific changes in GAP messenger RNA during regeneration will be observed using a cell-free synthesis system. The significance of these studies lies in their promise to reveal some molecular mechanisms which control axonal growth. These are of paramount importance in understanding the development of the nervous system, and its response to injury.